In blown plastic containers made by an extrusion blow molding process, it is common to form retention means on the finish by blow molding. Such retention means may comprise threads on the finish for engagement with threads on a closure. Where the retention means comprises a blow molded bead on the container, the compressive axial force of application of a closure by closure application machinery can collapse the finish. This may also occur where a container is made into a plastic tube by cutting off the base of the container after application of the closure. The axial force of application of the force coupled with the flexibility of the side wall of the container may result in inadequate retention of the closure. As a result, the desired off torque force is not maintained. It has been found that where the finish includes blown threads, when a closure is applied by closure application machinery, the controlled applied torque force collapses the finish and strips the closure off the finish. This occurs where the selected container finish and closure may not be fully compatible, that is, the threads and closures are imperfectly matched.
Among the objectives of the present invention are to provide a blown plastic container where the finish is sufficiently strong that it will not collapse when a closure is torqued or pressed onto a filled or unfilled container; where the closure will not readily strip off when being applied and the desired off torque will be maintained; and to provide a method of forming the finish to achieve such a result.
In accordance with the invention, the blown plastic container includes a hollow plastic body, an integral blow molded neck and an integral blow molded finish with a radially outwardly extending blow molded retention means such as thread or bead on the finish. In one form, the reinforcing means comprises blow molded axial columns extending radially outwardly. In another form, the reinforcing means comprises geometric depressions. Preferably, the reinforcing means are disposed circumferentially at equal spacing. When the extrusion blow molded container is trimmed, the finish may have an annular frustoconical radial ledge spaced from the open end of the finish. The projection means may extend between the ledge and the lowest mold threads or beads; between the threads or beads or for the full height of the finish above the ledge.